1. Field of the Invention
The present invention relates to a color display process, and more particularly, to a method of forming a color filter on a substrate having a thin film transistor (TFT) array.
2. Description of the Related Art
In recent years, liquid crystal displays (LCDs) of active matrix systems using thin film transistors (TFTs) have become attractive as high quality display apparatuses. In order to display a color image in the LCD, it is necessary to provide color filters of red, green and blue (RGB) to serve as light sources for generating the three primary colors.
For example, in a color filter LCD for a liquid crystal projector or a color LCD for direct viewing of a single plate type using one pixel (liquid crystal panel), color filters of the respective colors are provided. Thus, the respective colors of RGB correspond to pixels in a one-to-one manner.
In this instance, when the color filters of the respective colors of RGB are provided in one pixel region, it is necessary to provide a black matrix made of a light shielding film between the color filters of the respective colors.
A conventional color filter is formed on a second substrate arranged in such a manner that the substrate faces a first substrate on which the pixel driving elements have been formed so as to sandwich a liquid crystal layer. When such a structure is applied, however, it is difficult to eliminate a relative positional deviation between the first and second substrates. Therefore, it is necessary to increase the width of the black matrix by only an amount corresponding to a precise alignment of the first and second substrates. Consequently, the area of color filter is reduced and the area of display electrode used for displaying is also decreased.
Accordingly, a structure in which the color filters are formed on the side of the substrate on which the pixel driving elements are formed has been proposed. The color filter with this structure is called an on-chip color filter (also referred to as a color filter on array, COA structure). When the on-chip color filter is applied, the drawback caused by the foregoing alignment of the substrates can be avoided.
FIGS. 1Axcx9c1C show an example of previously proposed on-chip color filter processes disclosed in U.S. Pat. No. 6,162,544. In FIG. 1A, thin film transistor (TFT) structures 110 are formed on a glass substrate 100. A first planarization layer 120 is formed on the TFT structures 110. Contact windows 130 through the first planarization layer 120 are formed to expose a drain electrode 140 of each TFT structure 110. A transparent pixel electrode 150 is formed in each contact window 130 to electrically connect the drain electrode 140. Also, the pixel electrode 150 is extended on part of the first planarization layer 120.
In FIG. 1B, a second planarization layer 160 is formed to cover the pixel electrodes 150.
In FIG. 1C, a color filter 170 is formed on the second planarization layer 160 by, for example, a pigment dispersion method.
Nevertheless, the method of the prior art has some drawbacks that are described as follows:
(1). The steps of forming the contact windows 130, the pixel electrodes 150, and the color filter 170 require the performance of photolithography processes, thus, the fabrication of the conventional method is costly and complex.
(2). Because the color filter 170 is formed on the second planarization layer 160, the second planarization layer 160 must be transparent and have a small dielectric constant so that a coupling capacitor need not be formed between the color filter 170 and the pixel electrodes 150. Thus, the material selection of the second planarization layer 160 is difficult and the material cost of the second planarization layer 160 is high.
The object of the present invention is to provide a method of forming a color filter on a substrate having pixel driving elements.
Another object of the present invention is to provide a method of applying an inkjet method in a LCD process.
In order to achieve these objects, the present invention provides a method of forming a color filter on a substrate having pixel driving elements. A substrate having a plurality of light-transmitting areas and active areas is provided. A pixel driving element is formed on the substrate in each active area, wherein an insulation layer is formed between each pixel driving element and on the substrate in the light-transmitting areas. A planarization layer is formed on the pixel driving elements and the insulation layer. Part of the planarization layer is removed to form a plurality of contact holes and openings, wherein the contact holes expose part of the surface of the pixel driving elements, and the openings expose the surface of the insulation layer in the light-transmitting areas. At least one color pigment is filled into the openings to form a color filter on the substrate having the pixel driving elements. Transparent pixel electrodes are formed in the contact holes to electrically connect the pixel driving elements, wherein the transparent electrodes extend onto part of the color filter.
The present invention improves on the prior art in that the present method simultaneously forms the contact holes and the openings in the planarization layer, and then fills the color pigment into the openings to form a non-chip color filter. Thus, the invention forms the color filter without performing extra photolithography, thereby reducing costs and ameliorating the disadvantages of the prior art.